Process for the production of sulfur

ABSTRACT

SULFUR IS PREPARED BY THE SIMULTANEOUS INTRODUCTION OF HYDROGEN SULFIDE AND SULFUR DIOXIDE INTO AN AQUEOUS MEDIUM CONTAINING FROM 10 TO 120 GRAMS SODIUM CHLORIDE AND FROM 0.6 TO 85 GRAMS MAGNESIUM SULFATE PER LITER.

United States Patent O 3,595,966 PROCESS FOR THE PRODUCTION OF SULFURPierre A. Mathieu, Arthez-de-Bearn, France, assignor to SocieteNationale des Petroles dAquitaine, Paris, France No Drawing.Continuation-impart of applications Ser. No. 761,368, July 11, 1968, andSer. No. 805,044, Mar. 6, 1969, which are, respectively, continuationsof applications Ser. No. 520,204, Jan. 12, 1966, and Ser. No. 541,497,Apr. 11, 1966. This application Oct. 2, 1969, Ser. No. 863,379 Claimspriority, application France, Jan. 22, 1965, 3,085; Apr. 13, 1965,12,941 Int. Cl. C0111 17/04 US. Cl. 23-225R 4 Claims ABSTRACT OF THEDISCLOSURE Sulfur is prepared by the simultaneous introduction ofhydrogen sulfide and sulfur dioxide into an aqueous medium containingfrom to 120 grams sodium chloride and from 0.6 to 85 grams magnesiumsulfate per liter.

The process comprises the simultaneous introduction of hydrogen sulphideand sulphur-dioxide into an aqueous medium containing salts ofmonovalent ions and lesser amounts of salts of polyvalent ions, whichproduces sulphur of larger grain size and purity than has been possibleheretofore. This application is a continuationin-part of my patentapplication Ser. No. 761,368 filed July 11, 1968, and Ser. No. 805,044filed Mar. 6, 1969, which were, respectively, continuations of my patentapplications Ser. No. 520,204 filed Jan. 12, 1966, and Ser. No. 541,497filed Apr. 11, 1966, all now abandoned.

iIt is well-known that sulfur can be precipitated in an aqueous mediumby use of the so-called Claus reaction in accordance with the followingequation:

The aqueous medium can consist of water alone or of a solution of salts,such as chlorides, sulphates, etc., of sodium, potassium, magnesium,calcium, etc.

The prior art, recommended the use of concentrated saline solutions,either saturated (US. Pat. No. 1,995,545 of July 12, 1933) or verydiluted solutions containing, for example, 0.005 to 0.05 equivalent ofaluminum sulphate per liter as described in US. Pat. No. 2,563,437 ofMar. 24, 1949. The use of acid electrolytes has also been suggested inUS. Patent No. 2,563,437, supra, and in US. Pat. No. 2,534,063). Inpractice, the desulphuration yields of the gases thus treated at ambienttemperature, usually between and C. are good, but it is found that therate of recovery of the sulphur is reduced if the aqueous medium, afterseparation from the sulphur produced, is re-used several times insuccession. For example, when manufacturing sulphur by the reactionindicated above at a'temperature between 20 and 30 C., in saline Water,a desulphuration yield which is practically constant at about 85% isfound when the liquid is recycled after filtration of the sulphur, eachcycle lasting 3 hours. However, the rate of recovery of the sulphurfalls from 88% at the start to after the liquid has been recycled fourtimes. Furthermore, it is found that the speed of sedimentation of thesulphur falls in proportion as the liquid is recycled; the sulphurbecomes increasingly more colloidal. These and other difiicultiesexperienced with the prior art methods have been obviated in a novelmanner by the present invention.

It is, therefore, an outstanding object of the present invention toproduce a process for the production of sulfur in which it is possibleto recycle the aqueous medium Without reduction of yield.

"ice

Another object of this invention is the provision of a method ofproducing sulfur which can be carried on continuously without loss ofefficiency.

A further object of the present invention is the provision of asulfur-yielding process in which the sulfur obtained shows excellentsedimentation and is deposited immediately upon being formed.

It is another object of the instant invention to provide a process forthe production of sulfur in which the rate of recovery of sulfur ismaintained at a predetermined value.

With the foregoing and other objects in view which will appear as thedescription proceeds, the invention resides in the combination andarrangement of steps and in the details of operation hereinafterdescribed and claimed, it being understood that changes in the preciseembodiment of the invention herein disclosed may be made within thescope of what is claimed without departing from the spirit of theinvention.

SUMMARY OF THE INVENTION In general the process of the present inventionconsists in passing hydrogen sulphide and sulphur dioxide (optionallybut not essentially in the presence of gaseous hydrocarbon gas) into anaqueous medium containing an electrolyte consisting of monovalent anionsand cations and a further electrolyte consisting of polyvalen-t anionsand cations.

More specifically, there are two critical features of the presentinvention. The sulphur dioxide and the hydrogen sulphide are introducedinto the aqueous medium simultaneously in contrast to the practice ofthe prior art wherein the hydrogen sulphide was first dissolved in theaqueous medium and sulphur dioxide added subsequently thereto. It is afurther critical feature of the invention that the total concentrationof polyvalent ions be less than the total concentration of monovalentanions.

DESCRIPTION OF THE PREFERRED EMBODIMENT [[n accordance with thepreferred embodiments of the present invention there is prepared anaqueous solution containing polyvalent, suitably divalent anions andcations and monovalent anions and cations in such a manner that theratio of total polyvalent ions to total monovalent ions is always lessthan 0.75:1. Where C represents the total concentration of polyvalentions and C represents the total concentration of monovalent ions, thepreferred ratio of C zC is 0.05:1 to 0.75:1 most suitably between 0.1:1to 0.5 :1.

Any salts may be used as ion sources in the aqueous medium provided thatthe medium produced thereby is substantially neutral. Thus, there may beused as a source of monovalent ion alkali metals such as sodium,potassium or lithium; also suitable are strong nitrogenous bases such asthe ammonium anion. In association with these anions may be utilized themonovalent cations of acids, such as the chloride or nitrate ion.

With respect to the polyvalent ions, there may be utilized the ions ofthe alkaline earth metals such as calcium, or magnesium or trivalentanions such as aluminum or iron; tetravalent ions may also be utilized.Associated with these anions may be the cations of strong acid such assulphate, sulphi-te, phosphate, polythionate and the like. Thus,virtually any common combination of monovalent and polyvalent anions andcations may be utilized provided that they yield a substantially neutralaqueous solution.

Especially preferred, however, is the combination of monovalent ionssupplied by sodium chloride together with the polyvalent ions suppliedby magnesium sulphatc. This combination being especially preferredbecause of its essential cheapness rather than specific technicaladvantages supplied thereby. In fact, such a combination is present insea water which contains an approximate concentration per liter of 27grams of sodium chloride, 1 gram of potassium chloride, 4 grams ofmagnesium chloride and 1.7 grams of magnesium sulphate. Thisconcentration falls within the limits of the concentration of thepresent invention and thus provides a readily accessible and inexpensivesource of aqueous media for the practice of the present invention.

Certain experiments were carried out to compare the preparation ofsulfur by reacting H S with S by the method described in US. Pat. No.1,995,545 and by the method of the present invention.

Into a glass reactor of 3 liters, provided with a turboagitator rotatingat 2300 r.p.m., with an inlet tube for gas reaching the bottom of thereactor, and an outlet tube for the gas, 2 liters of water wereintroduced, which contained an amount of electrolyte indicated belowunder Al to A4 and B1 to B4.

Two series of experimentswere performed at room temperature:

Series A While the turbo-agitator rotated, a current of 33 liters perhour of 10% H by volume containing butane was passed for 3 hours throughsaid water. Subsequently, still under stirring, at current of 17 litersper hour of 5% by volume S0 containing butane was passed for 3 hoursthrough the above water which has absorbed H 5. As soon as passing thegas and stirring were stopped, the sedimentation of formed sulfur wasobserved: the time was noted until no longer sulphur particles were seenfalling onto the layer of sulphur deposited on the bottom of thereactor. If that time was t seconds and the height of the liquid layerabove the sulphur deposit was 1 millimeters, the velocity ofsedimentation V was calculated as V- (1 :t) mm./sec.

The operation was repeated with four different aqueous media,constituted by water having dissolved therein:

Al29.2 g. NaCl (0.5 equivalent) per liter;

A2-29.2 g. NaCl (0.5 equivalent) and 60.2 g. MgSO,

(1 equivalent) per liter;

A3-29.2 g. NaCl (0.5 equivalent) and 6 g. MgSO (0.1

equivalent) per liter;

A4l g. NaCl (0.017 equivalent) per liter.

Series B While the turbo-agitator rotated a gaseous current of butanecontaining by volume H 5 and 5% S0 was passed through the water during 3hours. Then the sedimentation of sulphur was observed, and its velocitywas calculated in the same manner as in the experiments of Series A.

The operation was repeated with the following four different electrolyteconcentrations in the water used:

B1-29.2 g. NaCl (0.5 equivalent) per liter;

B-2-29.2 g. NaCl (0.5 equivalent) and 60.2 g. MgSO,

(1 equivalent) per liter;

B329.2 g. NaCl (0.5 equivalent) and 6 g. MgSO (0.1

equivalent) per liter;

Cir

4 B4-l g. NaCl (0.0l7 equivalent) per liter.

The results obtained in each of the above runs are set forth in thefollowing table.

TABLE V, min/see. Supernatant liquid 7 Almost clear.

Clear.

Cloudy.

Very cloudy (colloidal solution). Clear.

Cloudy.

Clear.

Very cloudy (colloidal solution) Clearing by filtering the supernatantliquid in runs A3 and 8-2 was rather difficult, while it was quiteimpossible with A4 and B4, due to the colloidal nature of these liquids.

In Series A, the best result is obtained in run A2 which confirms theopinion expressed in US. Pat. No. 1,995,545 as to the usefulness of theaddition of magnesium sulphate. However, runs A4 and B4 show that a verysmall amount of NaCl (0.017 equivalent) is not sulficient.

On the other hand, these tests show that when the reactants H S and S0are simultaneously introduced into the aqueous medium (Series B), asurprising result is noted. While in Series A best results are obtainedin A2 (i.e., with an excess of magnesium sulphate over sodium chloride),and poorer results in A3 (with an excess of NaCl over MgSO in Series B(i.e., with simultaneous addition of the reactant gases), in B3 wherethere is excess NaCl over MgSO the sedimentation rate is the greatest ofall the test runs. Thus it is clearly demonstrated that the best resultsare obtained using simultaneous addition of the reactant gases into asolution containing sodium chloride together with but in excess ofmagnesium sulphate.

The other operative conditions for the preparation of sulphur from H 5and S0 are generally known b the prior art, and they also apply to themethod according to the invention. Nevertheless, said method may becarried out in ambient temperature with a very vigorous agitation.

In order that the invention may be more clearly understood, thedescription is illustrated hy the following series of examples given byway of non-limiting embodiments of the invention.

EXAMPLES 1 TO 7 The tests are carried out in a reactor of 3 liters,provided with a Moritz turbo-agitator rotating at 2300 revolutions perminute, an inlet tube for the gaseous mixture to be treated, reaching tothe bottom of the reactor, and an outlet tube for the gas. Into thereactor is introduced 2000 ml. of aqueous medium, at the bottom of whichis introduced a gaseous current constituted by a mixture of butane, H 5and S0 whilst the turbo-agitator rotates at the above-mentioned speed.The liquid is at ambient temperature. The gas is made to pass at therate of l./h. for 3 hours; at this moment, the latter is separated bydecantation in order to be used again, the speed V of this decantationis noted; its magnitude, expressed in mm./sec., is indicated in thefifth column of the following table.

TABLE l 1128, S02, '\',mm./ Example No. percent percent Liquid sec.

5 2. 5 Sea water 0. 1 Clear supernatant liquid. 10 1. 1 Do. 20 1. 0 D0.30 0. 9 Do. 10 5 0. 8 D0. 10 5 Distilled water 0. 3 Cloudy medium.

5 Water plus 0.5% NaCl, 1% MgS0l.. t). 7 Very cloudy medium.

In tests Nos. 1 to 4, variable contents of H 8 and S in the butane showthat the precipitated sulphur settles substantially at the same speed,Whatever may be the concentration in H of the gas treated. The yieldsvary from 35 to 95%. In test No. 5, the liquid used was an aqueoussolution of 35 g. NaCl per liter; the sulphur obtained settled somewhatmore slowly. Control test No. 6, carried out with distilled water led toa much slower sedimentation of the sulphur; moreover, the separatedliquid was cloudy and contained colloidal sulphur. On the other hand,while the suspensions of S of Examples 1 to 5 filter easily without anyclogging of the filter cloth, a rapid clogging took place in the case oftests Nos. 6 and 7.

EXAMPLE 8 The reactor of the preceding examples is set up with a view tocontinuous working; it is provided with an overflow at its upper partand with a supplementary tube, reacting to the bottom, for thecontinuous introduction of liquid. Into the reactor there is passed, perhour, 40 liters of mixture of methane and nitrogen, containing by volumeof H 8 and 5% 80;, the turbo-agitator turning at 2500 revolutions/ min.2000 ml. of sea water are introduced initially into the apparatus. Fromthe time when the reactor contents are constituted by an aqueoussuspension of 285 g. of sulphur per liter, the introduction of sea wateris commenced from the decantation of a preceding operation; thesuspension running from the overflow is collected and decanted. Theliquid thus separated is reintroduced into the reactor with a slightaddition of fresh sea water, required to compensate for the small amountof liquid retained in the cake of sulphur, obtained from the decantationsediment, after filtration. On the average, the decantation is done at aspeed of 1.2 mm./sec. The average yield of sulphur collected, withrespect to H 5, is 93%.

Further research which led to the present invention showed that theaforementioned difficulties previously encountered in the manufacture ofsulfur, were due, at least to a major extent, to the formation ofpolythionic acids; it is in this form that a fraction of the sulfurbeing used is lost. Another unexpected discovery is the fact that theformation of polythionic compounds is reduced when the temperature ofthe reaction medium is maintained around 50 C. and in practice in therange from 45 to 65 C. The process carries out the CLAUS reaction in anaqueous medium at a temperature which is in the range from 45 to 65 C.,preferably as close as possible to 50 C. At this last-mentionedtemperature, it is possible to obtain recovery rates of the sulfur inthe order of 90 to 98%, and these rates do not change when the liquid isrecycled.

Another feature of the invention lies in controlling the liquid mediumin which the precipitation of the sulfur is taking place from the pointof view of its acidity, so that the latter does not exceed the value of0.04 equivalent per liter. It has actually been found that, during themanufacturing operation, where recycling of the liquid is used, theaqueous medium gradually becomes acid and this results in poor totalyield and slow sedimentation. According to the invention, the medium isneutralized so as to avoid its pH value falling below 6; the pH ispreferably kept at a value which is in the range between 6 and 7.

The neutralization of the liquid medium is preferably brought aboutafter the separation and before the recycling of the liquid; asneutralizing agents, it is possible to employ known bases, butpreferably insoluble agents, such as lime or calcium carbonate, whichlead to salts which are only slightly soluble.

It is to be understood that the neutralization carried out in accordancewith the present invention is effective on all the liquid within which H8 and S0 are to react, and not only on a fraction intended to absorb theH 8, such as provided for in certain publications of the prior art, suchas U.S. Pat. No. 1,900,398.

The first of the characteristics of the new process, namely, theoperation carried out between 45 and 65 C., represents an improvement,both in connection with the process which does not use the recycling ofthe liquid medium and that in which this liquid is used again. In thislatter case, the second feature, namely, the control of the acidity ofthe medium, is particularly important.

The improved process in accordance with the invention can be applied toany of the known variants of the prior art process carried out in liquidmedium; particularly favorable results are obtained when thisimprovement is employed in the process in which the liquid medium isformed by water containing the certain well-defined porportions ofelectrolytes set forth above, and, more especially, sodium chloride andmagnesium sulphates. It is especially appropriate to use sea water asthe liquid medium for the precipitation of sulfur.

One aqueous medium which is very suitable for carrying the inventioninto effect contains, per liter, 0.2 to 2 equivalents or preferably 0.4to 1.2 equivalents of a monovalent electrolyte, particularly NaCl, KCl,LiCl or NH Cl, and 0.01 to 1.4 equivalents of polyvalent electrolyte,for example, MgSO the ratio between this second concentration and thefirst is generally in the range from 0.05 to 0.75 and is preferably inthe range from 0.1 to 0.5.

In carrying out the process according to the invention, each of thereagents, H 8 and S0 can be bubbled into the liquid medium separately,or these gases can be mixed together before coming into contact with theliquid. It is essential to achieve a gas/liquid dispersion which is asfine as possible. This result can be obtained, for example, by the useof turbo-stirrer, of the Moritz type, or an agitator of the Bicone type.The efficiency of the agitator can be increased by providing baffleplates in the reactor. The agitation or stirring speeds are preferablybetween 1500 and 5000 rpm, depending on the type of agitator being used;it is desirable to use the highest possible speeds.

The invention is further illustrated by the following examples. Thetests specified in these examples all had in common the followingelements: they were carried out in a three-liter reactor equipped with aMoritz stirrer mechanism, a supply pipe for the gaseous mixture to betreated extending to the bottom of the reactor, and a gas outlet tube.The stirrer mechanisms rotated a 2300 r.p.rn. in each test, the liquidcontents of the reactor consisted of two liters of sea water, thegaseous mixture consisting of by volume of butane, 10% by volume of H 8,and 5% by volume of S0 the rate of flow of this gas Was 50 liters perhour.

In the tables, the following symbols are used:

Nr: number of recyclings Rd: desulfuration yield Rs: sulfur recoveryyield Rg: total yield Vs: sulfur sedimentation speed EXAMPLE 9 Thisprocess was carried out at ambient temperature. Each test lasted 3hours, after which the sulfur was filtered and the liquid was used againin the following test. Table II gives the results of this series of 5successive tests.

TABLE II Nr percent percent percent 7 EXAMPLES 10-16 Each of theoperation of these examples was carried out with fresh sea water, but ata different temperature.

TABLE III Tempera- Rd, Rs, Ry, Example N0. ture, C. percent percentpercent 84. 5 88 74. 8 80 86 74 86. 5 96 83 86 03 8O y 82 s3 (is 70. 579. 5 50 00 65 83 54 It is apparent from Table III that it is at 50 C.that the sulfur recovery yield Rs is at its best, reaching in fact 96%at this temperature. The sedimentation then reaches 1.2 mm./sec. and thepurity of the sulfur is from 99.6 to 99.8%.

EXAMPLE 17 A series of operations was carried out at 50 C., the aqueousliquid being recycled each time in order to be used again in thefollowing test. Each test lasted 3 hours, as before.

TABLE IV Rd, Rs, R9, N1 percent percent percent V s 86 91 78 1mm./sec.86 97.5 84 0.2 FURL/S00. S9 00 80 0.05. 80 01 83. 5 S8 97 85. 5 87 01 5S0 80 Very slow. 88 07 85. 5

& g? }Suliur colloidal.

It can be seen from the figures of Table IV that the sulfur recoveryyield remains high and fairly constant after the recycling operations,but the sulfur sedimentation speed, Vs, is quickly reduced; from thesecond recycling, it becomes very low; in addition, the liquid containscolloidal sulfur.

EXAMPLE 18 In a series of tests similar to those of Example 17, at 50C., the acidity of the liquid medium after each separation of theprecipitated sulfur was determined; it was found to be close to 0.3eq./l. This medium was then neutralized with lime to pH 6 before beingused again in the following test.

The following Table V gives the results of these tests.

It is seen that, at 50 C., in a sea water medium at pH 6, the sulphurrecovery yield is high, being 91 to and does not fall after therecycling operations carried out on the liquid; the sedimentation speedis very high and the desulfuration yield remains invariable in theregion of 86%.

8 EXAMPLE 19 The reactor of the previous examples was arranged forcontinuous working; it was equipped with an overflow device at its upperend and a supplementary pipe extending downwardly to the bottom for thecontinuous introduction of the liquid.

50 liters per hour of a mixture of methane and nitrogen containing byvolume 10% of H 5 and 5% of S0 were caused to enter the reactor, thestirring mechanism rotating at 2500 r.p.m. 200 ml. of sea Water wereinitially introduced into the apparatus. From the moment when thecontent of the reactor was formed by an aqueous suspension of sulfur, ofwhich the acidity was in the region of 3 10 equivalent/ liter, there isinitiated the introduction thereinto of sea water originating from thedecantation of a previous operation, the pH of this liquid having beenbrought to 6. The suspension leaving the system in the liquid by way ofthe overflow device was collected, decanted and neutralized.

The decanted and neutralized liquid was reintroduced into the reactorwith the slight addition of fresh sea water which was necessary tocompensate for the small amount of liquid retained in the sulfur cakeobtained from the decantation sludge after filtration. The sedimentationof the sulfur was practically instantaneous, while the sulfur recoveryyield was on average 96%.

Thus, due to the improvement provided by the invention, sedimentationspeeds of the order of 1 mm./s. are regularly effected. The sulphurdeposits obtained according to the invention are easily filtrable, andyield a cake having a low water content, which results in the advantageof facilitating subsequent operations, such as transport, drying, oreven direct fusion of the sulphur, under pressure; in the case of such afusion, very pure sulphur is obtained, at least 99.8% in spite of thepresence of the aqueous phase containing electrolytes.

While it will be apparent that the illustrated embodiments of theinvention herein disclosed are well calculated adequately to fulfil theobjects and advantages primarily stated, it is to be understood that theinvention is susceptible to variation, modification, and change withinthe spirit and scope of the subjoined claims.

The invention having been thus described, what is claimed as new anddesired to secure by Letters Patent is:

1. A process for the preparation of sulfur which comprisessimultaneously introducing hydrogen sulfide and sulfur dioxide into anaqueous medium containing from 10 to grams sodium chloride and from 0.6to 85 grams magnesium sulfate per liter.

2. The process of claim 1, wherein said medium contains from 20 to 50grams sodium chloride and from 1 to 10 grams magnesium sulfate perliter.

3. The process of claim 1, wherein said aqueous medium is constituted ofsea water.

4. The process of claim 1, including the steps of (a) maintaining thetemperature of said medium in the range from 45 C. to 60 C. and (b)controlling the acidity of said medium so that it does not exceed 0.04equivalent of acid per liter.

References Cited UNITED STATES PATENTS 1,079,291 11/1913 Feld 23-2251,832,448 11/1931 Coleman et a1. 23-225 1,917,351 7/1933 Young 232261,995,545 3/1935 Leahy 23-225 OSCAR R. VERTIZ, Primary Examiner G. O.PETERS, Assistant Examiner

